Musnad Ahmad 27:1527

Abd al-Samad narrated to us, Hammad narrated to us, Thabit narrated to us, from Ibn Umar, that the Messenger of Allah (peace and blessings of Allah be upon him) said to a man: "Did you do such and such?" He said: "No, by the One besides Whom there is no god, O Messenger of Allah, I did not do it." He said: "Yes, you did do it, but you have been forgiven due to [your] sincerity."